MFD Coolant warning. Replaced the coolant tank and sensor, still there. What now?

I have an '09 TSI MKV, 89k miles.

As the title says. This doesn't go away with time as the engine warms up, the coolant symbol still flashes on the MFD throughout the drive.

I chalked it up to a faulty sensor, so I went ahead and replaced the tank this weekend. The warning still persists. Coolant level is good, I only used G12.

I got a tip through searching to open and close the tank cap to let some pressure release. I did notice that if I did that, the warning takes a while longer during the drive to show up. I've done this repeatedly already. At the moment, the warning shows maybe 10 seconds after the car is turned on. For whatever that's worth. I'll open the cap up again next time I'm driving.

Provided that the problem doesn't go away, what else should I be checking or assuming?